u 


THE  PREPARATION  OF  MONO- 
BROMACETIC  ACID  AND  ITS 
ESTER 


BY 

ROBERT  T.  REED 


THESIS 

FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CHEMISTRY 


COLLEGE  OF  LIBERAL  ARTS  AND  SCIENCES 

UNIVERSITY  OF  ILLINOIS 


1!)22 


. 


Digitized  by  the  Internet  Archive 

in  2016 


https://archive.org/details/preparationofmonOOreed 


ACKNOWLEDGMENT 


The  author  wishes  to  express 
his  sincere  thanks  to  Dr.  B.  L.  Souther 
for  his  valuable  help  and  direction 
throughout  this  investigation. 


* . . 


. 


TABLE  OE  CONTENTS 


Page 


Introduction 1 

Historical 2 

Experimental 6 

Summary.  9 

Bibliography 10 


•1 


INTRODUCTION 

Bromacetic  acid  is  not  a commercial  product,  "but  is  used 
to  some  extent  in  the  laboratory  in  carrying  out  the  Reformatsky 
Reaction.  This  is  a reaction  between  zinc,  an  aldehyde,  and  brom- 
acetic ester  to  give  a B-hydroxy  ester  which  wrhen  hydrolyzed  gives 
the  B-hydroxy  acid. 

Chloracetic  acid^  is  made  commercially  and  used  to  a great 
extent  in  the  preparation  of  indigo  from  aniline.  It  is  made  by 
passing  dry  chlorine  gas  through  glacial  acetic  acid.  A small  amount 
of  acetic  anhydride  is  added  to  act  as  a catalyzer.  This  method  givei 
a very  good  yield  and  it  was  conceived  that  bromacetic  acid  might  be 
prepared  in  the  same  manner. 


2 


HISTORICAL 

Mono -bromacetic  acid  has  teen  prepared  in  many  different 
ways  to  get  a product  free  from  impurities  and  also  free  from  di-  and 
tri-bromacetic  acids.  Another  difficulty  has  been  to  get  a good  yield 
from  the  reaction. 

One  of  the  methods  very  commonly  used  is  employing 

p 

phosphorus^  as  a catalyzer.  The  use  of  phosphorus  as  a halogen 
carrier  was  first  discovered  by  Corenweinder.  It  was  later  found  by 
Personne  that  red  phosphorus  worked  better  than  yellow  phosphorus  or 
a mixture  of  the  two.  The  bromination  of  acids  in  the  presence  of 
phosphorus  was  first  discovered  by  a German  chemist  named  Hell.  One 
necessity  in  using  phosphorus  is  that  all  materials  be  dry,  therefore 
since  red  phosphorus  always  contains  a little  phosphoric  acid,  the 
acid  must  be  washed  out  and  then  the  red  phosphorus  dried  again.  For 
every  mole  of  acetic  acid  used  about  5 grams  of  red  phosphorus  were 
used.  The  pip  cess  was  carried  out  in  a reflux  condenser.  The  bromin 
was  forced  through  the  acetic  acid  as  a gas.  The  reaction  was  heated 
over  a water  bath  and  in  direct  sunlight.  The  sunlight  seemed  to  act 
as  a catalyzer  since  the  reaction  went  much  faster  when  it  was  used. 
The  total  time  for  it  to  go  to  completion  was  between  one  and  two 
days.  The  bromacetic  acid  was  recovered  by  distilling  under 
diminished  pressure.  It  came  over  at  a temperature  of  110°  U.  under 
50  mm.  pressure.  The  difficulty  with  this  reaction  was  that  the 
product  after  distillation  was  a very  sluggish  mixture  from  which  it 
was  difficult  to  extract  the  final  product.  Another  difficulty  i3 
that  often  the  bromacetic  acid  has  sorae  di-  and  tri-bromacetic  acid 


in  it 


. 


. 


-3 


Use  of  Phosphorus  Pen tabromide 

3 

When  phosphorus  pentabronide  was  used,  the  reaction  w s 
carried  out  in  a similar  manner  as  in  the  case  when  only  phosphorus 
was  used.  Acetyl  "bromide  was  first  generated  and  then  the  anhydride 
was  formed  which  reacted  with  hydrobromic  acid  to  give  one  molecule 
of  bromacetic  acid  and  one  molecule  of  acetyl  bromide.  The  acetyl 
bromide  reacted  again  with  more  acetic  acid  to  give  more  of  the 
anhydride.  This  reaction  went  fairly  smooth,  but  it  also  gave  a 
sluggish  mixture  which  was  very  hard  to  work  with. 

The  reactions  were  as  follows: 

1.  P 4 Br^  — P Br5 

2.  CH3  COOH  4 P Br-  -*■  CHS  COBr  + POBr3  4 HBr. 

3.  CH3  COBr  + CK3  COOH  — CH3  qo  + H Br 

,0 

CH3  CO 


4 CHpO 

!o  + Br,  — 
CHpO 

5.  CH*  BrCO 

0 4 H Br 

CH3C0 


CHg  BrCO 

04  E Br 
CH3CO 


CHa  BrCOOH  4 CH3  CO  Br 


Preparation  of  Mono -Bromacetic  Acid 
Using  Sulphur  as  a Catalyzer  (4) 

A reflux  condenser  was  used  into  which  five  parts  of 
sulphur  were  added  for  every  one  hundred  parts  of  acid  used. 

The  bromine  was  added  in  small  portions,  using  a small  excess  of 
the  theoretical  amount.  After  the  reaction  was  complete  which  was 
shown  by  the  fact  that  no  more  hydrogen  bromide  gas  was  being 
given  off,  the  mixture  was  distilled  under  atmospheric  pressure. 


.4 


The  acid  distilled  over  at  207°  C.  and  crystallized  immediately. 

The  objection  to  this  method  was  that  di-bromacetic  acid  was  found 
unless  extreme  precautions  were  taken.  As  soon  as  an  excess  of  the 
theoretical  amount  of  bromine  was  added  the  mono -bromacetic  acid 
would  react  with  it  to  give  the  di-bromacetic  acid.  It  was  very 
hard  to  add  just  the  theoretical  amount  of  bromine  because  it  was 
never  known  how  much  bromine  had  escaped  during  the  reaction.  Some 
compounds  were  formed  by  the  reaction  of  bromine  on  the  sulphur. 

This  not  only  cut  down  the  yield  but  these  compounds  were  very  hard 
to  get  rid  of  when  the  pure  bromacetic  acid  was  recovered. 

Process  of  Heating  Bromine  and  Acetic 
Acid  in  a Closed  Tube  5 

Equal  portions  of  glacial  acetic  acid  and  bromine  were 
heated  in  a closed  tube  to  the  temperature  of  150°  C.  When  the 
solution  became  colorless  or  an  amber  color,  the  tube  was  then 
cooled  thoroughly  and  broken.  A large  amount  of  hydrogen  bromide 
escaped.  The  residue  was  then  placed  in  a retort,  or  reflux 
condenser  and  boiled  until  all  of  the  hydrogen  bromide  gas  had  been 
given  off.  This  was  told  by  passing  the  gas  through  silver 
nitrate  solution.  The  solution  then  contained  bromacetic  acid, 
di-bromacetic  acid,  and  a little  hydrogen  bromine.  The  mixture 
was  then  heated  to  150°  C.  and  CO2  gas  was  passed  through  it  until 
the  very  last  traces  of  hydrogen  bromide  gas  were  given  off.  An 
excess  of  lead  carbonate  and  10  times  its  volume  of  water  were  then 
added  to  the  acid  and  the  solution  was  heated  to  100°  C.  and  allowed 
to  stand  for  a few  hours.  After  standing  the  liquid  was  filtered 
from  the  separated  crystalline  precipitate.  The  crystals  v/ere 


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washed  with  cold  water  and  then  suspended  in  water  into  which 
hydrogen  sulphide  was  conducted  until  the  solution  was  saturated. 
The  liquid  when  filtered  and  concentrated  gave  the  pure  crystalline 
acid.  The  latter  part  of  this  preparation  was  a method  of 
separating  the  bromacetic  acid  from  the  di-brornacetic  acid.  The 
lead  salt  of  the  dibrom  acid  is  far  more  soluble  than  that  of  the 
mono -bromacetic  acid. 


■ - 


. 


■ 


-6- 


EXPERIMENTAL 

In  all  of  these  reactions  acetic  anhydride  was  used  as  a 
catalyzer.  It  must  he  free  from  water.  Common  acetic  anhydride 
contains  a large  amount  of  acid,,  therefore,  it  must  he  distilled 
before  using.  The  advantages  of  acetic  anhydride  were  that  it  did 
not  give  a mixture  of  the  mono-  and  di-bromacetic  acids  and  also 
the  final  product  was  easily  recovered. 

The  first  reaction  was  run  using  a common  round  bottom 
flask  with  a rubber  stopper  connection  to  the  condenser.  The 
bromine  reacted  very  violently  with  the  rubber  and  at  the  end  all 
that  was  left  was  a gummy  mass  from  which  it  was  impossible  to 
recover  the  bromacetic  acid.  A glass  stoppered  flask  and  condenser 
were  then  obtained.  This  was  a great  advantage  in  that  there  was 
no  rubber  to  react  with  the  bromine  and  it  also  made  a water  tight 
connection.  A little  water  would  ruin  the  reaction  because  the 
acetic  anhydride  would  react  with  it  to  give  acetic  acid.  From  the 
top  of  the  condenser  the  hydrogen  bromide  gases  were  passed  over 
water  and  absorbed.  This  prevented  their  escape  into  the  room, 

120  grams  of  glacial  acetic  acid  and  lOcc.  of  acetic 
anhydride  were  first  placed  in  the  flask  to  which  160  grams  of 
bromine  were  added.  The  flask,  heated  by  means  of  a water  bath, 
was  heated  very  slowly  at  first.  This  prevented  the  reaction,  which 
was  violent  at  first  from  boiling  over  the  top  of  the  condenser. 

A red  substance  crystallized  out  in  the  condenser  but  after  the 
reaction  had  gone  for  sometime  before  these  crystals  melted. 

They  were  probably  bromacetic  acid  crystals  with  some  bromine 
mixed  in  with  them. 


-7- 


Aftsr  the  reaction  had  gone  for  2 hours  the  solution 
assumed  a light  yellow  color.  This  was  due  to  the  fact  that  all  of 
the  "bromine  had  reacted.  Another  portion  of  160  grams  of  "bromine 
was  added  and  the  solution  was  again  heated  very  slowly.  The  water, 
however,  was  kept  "boiling  constantly  after  it  was  started.  When 
the  refluxing  had  gone  for  another  2 hours  the  solution  again  became 
colorless.  Since  the  theoretioal  amount  of  bromine  had  been  added 
it  assumed  that  the  reaction  was  complete.  However  upon  extracting 

i 

the  pure  bromacetic  acid,  the  yield  was  found  to  be  only  56 %,  From 
these  results  it  was  concluded  that  44#  of  the  bromine  had  escaped 
and  not  reacted. 

In  the  next  run  an  excess  of  44#  of  bromine  was  added  in 
three  portions  af  about  154  grains  each.  The  first  two  portions  were 
not  added  until  the  solution  became  colorless,  when  no  more  hydro geii 
bromide  gas  was  given  off  after  the  last  portion  had  been  added  the 
reaction  was  considered  to  be  complete.  The  time  for  one  complete 
reaction  was  between  7 and  8 hours. 

The  pure  bromacetic  acid  was  recovered  by  distilling  the 
mixture  unaer  diminished  pressure.  First,  the  excess  bromine 
distilled  over  followed  by  the  acetic  acid  which  did  not  react. 
Finally,  at  a temperature  of  about  105-108°  C.  and  under  a pressure 
of  50  mm.  a colorless  solution  began  to  distill  over.  It  solidified 
as  soon  as  it  came  in  contact  with  the  cold  receiving  flask. 

The  product  under  ordinary  conditions  is  a colorless 
crystalline  substance  which  melts  at  50°  C.  and  boils  at  208°  u. 

It  has  little  or  no  odor  when  free  from  hydrogen  bromide.  when  a 
little  of  it  gets  on  the  hands  it  is  hardly  noticed  at  the  time  but 
the  next  morning  there  will  be  a large  blister  there.  It  is  very 


-8- 

painful  then  and  will  be  an  open  sore  for  a few  days. 

Nine  runs  were  made  using  practical ly  the  same  amounts 
as  stated  before.  The  yields  ran  between  72$  and  87.21$  of  the 
theoretical  yield.  The  theoretical  yield  was  calculated  from  the 
amount  of  acetic  acid  that  was  used.  The  be3t  yield  of  255  grams 
of  pure  bromacetic  acid  was  obtained  by  using  120  grams  of  acetic 
acid,  467  grams  of  bromine,  and  lOcc.  of  acetic  anhydride.  The 
theoretical  yeidl  from  acetic  acid  was  278  and  from  the  acetic 
anhydride  it  was  14.4  making  a total  yield  of  292.4  grams. 


fin- ' 87 -21* 

At  first  it  was  thought  that  the  work  on  bro.macetic  acid 
would  be  short  enough  to  allow  for  some  work  on  the  ester  but  it 
was  found  that  the  whole  semester  was  taken  up  -with  the  work  on  the 
acid. 


SUMMARY 

It  was  found  that  hromacetic  acid 
could  be  prepared  in  good  yields  by  using 
acetic  anhydride  as  a catalyzer. 


' 


. 

. 


-10- 


B IBL 10  GRAPHY 


1.  Martin.  Industrial  Chemistry,  Organic,  vol.  1,  page  332. 

2.  Gattermann,  Practical  Methods  of  Organic  Chemistry,  Page  163 

3.  Gattermann,  Practical  Methods  of  Organic  Chemistry,  page  165 

4.  Bulletin  de  la  Societie  chimique  senes  3.  vol  7,  page  365 

5.  Annalen  der  Chimie.  Vol.  108,  page  106. 


